CVE-2026-33805

@fastify/reply-from vulnerable to connection header abuse enabling stripping of proxy-added headers

CVSS 9 CRITICALEPSS 0.3%CWE-644

Vexday Risk Score

28Low

SSVC decision (CISA)

Track

No exploitation signal → monitor

CVSS 9EPSS 0.3%KEV nãoPoC —Nuclei —Metasploit —Patch —

Lifecycle

15 Apr 2026Published on NVD

Recommendation: Monitor — no exploitation signal at the moment.

@fastify/reply-from v12.6.1 and earlier and @fastify/http-proxy v11.4.3 and earlier process the client's Connection header after the proxy has added its own headers via rewriteRequestHeaders. This allows attackers to retroactively strip proxy-added headers from upstream requests by listing them in the Connection header value. Any header added by the proxy for routing, access control, or security purposes can be selectively removed by a client. @fastify/http-proxy is also affected as it delegates to @fastify/reply-from. Upgrade to @fastify/reply-from v12.6.2 or @fastify/http-proxy v11.4.4 or later.

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N

Affected products

@fastify/reply-from · @fastify/http-proxy @fastify/reply-from · @fastify/reply-from

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References

https://cna.openjsf.org/security-advisories.html https://github.com/fastify/fastify-reply-from/security/advisories/GHSA-gwhp-pf74-vj37